The present invention relates to a magnetic head utilizing a magneto-impedance effect by which the impedance of a sensing conductor is varied by application of a magnetic field, and a magnetic recording and reproducing apparatus using the magnetic head.
An example of a magnetic reproducing head in the prior art is described with reference to FIG. 12A, FIG. 12B and FIG. 13. FIG. 12A is a perspective view of a magnetic reproducing head (hereinafter referred to as the MI head) utilizing the magneto-impedance effect (MI effect) in the prior art, described in IEICE Technical Report MR95-80.
In FIG. 12A, a magneto-impedance effect detector (hereinafter referred to as the magnetic detector) in a MI head 61 is configured by placing a thin film sensing conductor 42 of an electrically conductive metal thin film between two soft magnetic cores 46 and 47 each having a width 43 approximately equal to the track width of a magnetic recording medium 53. As shown in an enlarged view of FIG. 12B, the soft magnetic cores 46 and 47 are formed by alternately laminating permalloy films 44 and SiO2 films 45.
When the MI head 61 reproduces a signal magnetization 54 recorded on the magnetic recording medium 53, a high frequency carrier signal in the UHF band is applied from a high frequency oscillator 48 to the thin film sensing conductor 42 through a resistor 49, thereby flowing a high frequency current 50 therethrough. Then, a voltage change caused by the magneto-impedance effect is detected across terminals 51 and 52 connected to respective ends of the thin film sensing conductor 42. The easy magnetization axes of the soft magnetic cores 46 and 47 are initially oriented in a direction parallel to the width direction of the recording track of the magnetic recording medium 53.
When there is no signal magnetization 54 on the magnetic recording medium 53, a voltage of a high frequency carrier signal arises across the terminals 51 and 52, and the voltage value is equal to the product of the high frequency current 50 and the impedance between these terminals 51 and 52 of the thin film sensing conductor 42.
When there is a signal magnetization 54 on the magnetic recording medium 53, the easy magnetization axes of the soft magnetic cores 46 and 47 deviate from their initial direction of orientation because of the presence of the signal magnetization 54. As a result, the impedance across these terminals 51 and 52 of the thin film sensing conductor 42 decreases due to the magneto-impedance effect.
The high frequency carrier signal is amplitude-modulated according to the change in the impedance of the thin film sensing conductor 42 by the signal magnetization 54 on the magnetic recording medium 53, and thereby the signal magnetization 54 is detected. The signal magnetization 54 on the magnetic recording medium 53 can be read out by demodulating the amplitude-modulated signal.
The detection sensitivity of the signal magnetization 54 on the magnetic recording medium 53 based on the magneto-impedance effect is much higher than the detection sensitivity based on the magnetoresistive effect. The MI head utilizing the magneto-impedance effect has the possibility of producing an output about 10 times as high as that of the known giant MR head utilizing magnetic resistance which is in the process of development.
FIG. 13 is a characteristic curve showing the change in the high frequency carrier signal level with respect to the magnetic field applied to the MI head 61. In FIG. 13, the characteristic curve 56 is obtained by setting the frequency of the high frequency carrier signal at 1 GHz and varying the strength of DC magnetic field applied to the MI head 61 placed in the central portion of the known Helmholtz coil.
According to the characteristic curve 56, the rate of change of the high frequency carrier signal level is small at and near the point where the applied magnetic field strength is zero. In order to modulate the high frequency carrier signal with a high degree of modulation with respect to the change in the magnetic field strength and to obtain a high frequency amplitude-modulated signal with a low distortion, it is desirable to give a DC bias magnetic field 55 biasing the magnetic field so as to use the linear portion of the characteristic curve 56. In the above-mentioned MI head, a DC power supply 58 superimposes a DC current on the current of the high frequency carrier signal in order to produce the DC bias magnetic field 55. By flowing this DC current through the thin film sensing conductor 42, a DC magnetic field is generated to bias the magnetic field.
The change rate of the impedance of the sensing conductor caused by the magneto-impedance effect is proportional to the product of the frequency of the high frequency carrier signal applied to the sensing conductor and the rate of change of the magnetic permeability of the soft magnetic cores. In order to increase in the detection sensitivity by increasing the change rate of the impedance of the sensing conductor, permalloy films 44 having a large permeability change are used for the material of the soft magnetic cores 46 and 47 in the prior art MI head as mentioned above. A laminated film structure consisting of the permalloy films 44 interleaved with insulating SiO2 films 45 is employed in order to suppress eddy currents at high frequencies. Further, the frequency of the high frequency carrier signal is set at several hundred MHz or higher.
Accompanied by the increase of the magnetic recording density, the track width must be made narrower. As the track width becomes narrower, the strength of the signal magnetization decreases. The MI head in the prior art has no sufficient sensitivity with respect to such narrow track. Therefore, an MI head having a higher sensitivity is needed. An object of the present invention is to provide an MI head having a higher sensitivity than that in the prior art.
The MI head utilizing the magneto-impedance effect has a high reproduction sensitivity and is suitable for high density recording media. However, since the MI head is exclusively for reproducing, a separate recording head must be used for recording. Another object of the present invention is to provide a recording and reproducing head by adding a recording capability to a reproducing head utilizing the magneto-impedance effect.
A magnetic head of the present invention comprises: a first soft magnetic film formed on a non-magnetic substrate; a second soft magnetic film having a thickness smaller than the thickness of the first soft magnetic film, and formed on the substrate in contact with an end portion of the first soft magnetic film; an electrically conductive metal film formed on the second soft magnetic film; a third soft magnetic film having a thickness smaller than the thickness of the first soft magnetic film, and formed on the electrically conductive metal film so that an end portion of the third soft magnetic film contacts the first soft magnetic film; a magnetic path portion of a soft magnetic film formed on the substrate in contact with an end portion of each of the second and third soft magnetic films, and having a thickness greater than the thickness of each of the second and third soft magnetic films; and a return path yoke formed by facing to the magnetic path portion at one end portion thereof with a non-magnetic gap member interposed therebetween, contacting to the first soft magnetic film at the other end portion, and with a center portion thereof separated from the third soft magnetic film by a non-magnetic portion interposed therebetween.
When a high frequency current is passed through the electrically conductive metal film, the impedance of the electrically conductive metal film placed between the second and third soft magnetic films changes due to the magnetic flux passing through the first and second soft magnetic films by an external magnetic field. With this impedance change, the high frequency current is amplitude-modulated. By demodulating the amplitude-modulated current, the external magnetic field can be detected. In the above configuration, when the second and third soft magnetic films are made thinner than the first soft magnetic film, high density recorded signals can be reproduced with a high sensitivity.
A magnetic head in another aspect of the present invention comprises: a first soft magnetic film formed on a non-magnetic substrate; a second soft magnetic film formed in a region where a portion of the first soft magnetic film has been removed (hereinafter referred to as Z region), and extending over the remaining first soft magnetic film, the second soft magnetic film having a thickness smaller than the thickness of the first soft magnetic film; an electrically conductive metal film formed on the second soft magnetic film within the Z region; a third soft magnetic film formed on the electrically conductive metal film and the second soft magnetic film, and having a thickness smaller than the thickness of the first soft magnetic film; a non-magnetic insulating film as a gap member formed on a portion of the third soft magnetic film; a non-magnetic portion formed on the third soft magnetic film within a portion corresponding to the Z region; and a soft magnetic film as a return path yoke formed on the non-magnetic insulating film, the non-magnetic portion, and the third soft magnetic film.
By removing a part of the first soft magnetic film formed on the substrate, and by forming the second soft magnetic film, the electrically conductive metal film, and the third soft magnetic film in the part, the second and third soft magnetic films are formed so as to put the electrically conductive metal film therebetween. By means of the above-mentioned configuration, an external magnetic field can be detected based on the change in the impedance of the electrically conductive metal film through which a high frequency current passes, caused by the external magnetic field.
A magnetic head fabrication method of the present invention comprises the steps of: forming a first soft magnetic film on a substrate; forming a recessed portion by etching by means of an ion beam or the like a portion of the first soft magnetic film formed on the substrate until a substrate surface is exposed; forming a second soft magnetic film in the recessed portion to a thickness smaller than the thickness of the first magnetic film; forming an electrically conductive metal film on the second soft magnetic film in the recessed portion; and forming a third soft magnetic film on the electrically conductive metal film. In this fabrication method, a portion of the first soft magnetic film formed on the substrate is etched away by means of an ion beam or the like to form a recessed portion, and the magnetic head is obtained by putting the electrically conductive metal film between the second and third magnetic in the recessed portion.
A magnetic head fabrication method in another aspect of the present invention comprises the steps of: forming a first soft magnetic film on a non-magnetic substrate; removing a portion of the first soft magnetic film; forming a second soft magnetic film in a region where the first soft magnetic film has been removed (hereinafter referred to as Z region) and over the remaining first soft magnetic film; forming an electrically conductive metal film on the second soft magnetic film within the Z region; forming a third soft magnetic film on the electrically conductive metal film and the second soft magnetic; forming a non-magnetic insulating film as a gap member on a portion of the third soft magnetic film; forming a non-magnetic portion on the third soft magnetic film within a portion corresponding to the Z region; and forming a soft magnetic film as a return path yoke on the non-magnetic insulating film, the non-magnetic portion, and the third soft magnetic film. With this fabrication method, the magnetic head can be fabricated using thin film deposition technology, and the fabrication cost can be reduced.
A magnetic head in another aspect of the present invention comprises: a first magnetic film formed on a non-magnetic substrate; a second magnetic film formed on the first magnetic film and having a recessed portion in a part thereof; a third magnetic film formed at least in the recessed portion of the second magnetic film, and having a thickness smaller than the thickness of the second magnetic film; an electrically conductive metal film formed in the recessed portion; a fourth magnetic film formed so as to hold the electrically conductive metal film in cooperation with the third magnetic film; a return path yoke formed with a space to at least the face of the electrically conductive metal film, facing the fourth magnetic film with a predetermined magnetic gap at one end portion, and contacting the fourth magnetic film at the other end, an electrically conductive metal film winding formed passing through the space and to which a recording signal is applied at the time of recording; a high frequency signal generator connected to respective ends of the electrically conductive metal film, for applying a high frequency carrier signal at the time of reproduction; and a high frequency amplifier connected to the respective ends of the electrically conductive metal film, for demodulating a high frequency signal for output at the time of reproduction.
At the time of recording, the magnetic head serves as a recording head by applying a recording signal to the electrically conductive metal film winding. At the time of reproduction, a recorded magnetization is detected as a change in the impedance of the electrically conductive metal film by applying a high frequency carrier signal to the respective ends of the electrically conductive metal film. In this way, the magnetic head of the present invention can be used for both recording and reproducing operations.
A magnetic recording and reproducing apparatus of the present invention comprises: a magnetic recording and reproducing head having a first magnetic film formed on a non-magnetic substrate, a second magnetic film formed on the first magnetic film and having a recessed portion (Z region) in a part thereof, a third magnetic film formed at least in the recessed portion of the second magnetic film and having a thickness smaller than the thickness of the second magnetic film, an electrically conductive metal film formed in the recessed portion, a fourth magnetic film formed so as to hold the electrically conductive metal film in cooperation with the third magnetic film, a return path yoke formed in spaced relation to at least the face of the fourth magnetic film in a region including the electrically conductive metal film, facing the fourth magnetic film with a predetermined magnetic gap at one end portion, and contacting the fourth magnetic film at the other end, an electrically conductive metal film winding formed passing through the space and to which a recording signal is applied at the time of recording, a high frequency signal generator connected to respective ends of the electrically conductive metal film, for applying a high frequency current at the time of reproduction, and a high frequency amplifier connected to the respective ends of the electrically conductive metal film, for demodulating a high frequency signal for output at the time of reproduction; and a recording medium used for recording and reproduction with the magnetic recording and reproducing head.
Since the magnetic recording and reproducing head includes an electrically conductive metal film winding to which the recording signal is applied, the same head can be used for both recording and reproducing operation, and the apparatus can be simplified in construction.